test(bundlers): add node webpack tests, expand edge coverage, assert known protobuf failures

[overbalance]

Which problem is this PR solving?

The existing webpack bundler tests use browser-based HTML testing which is unnecessarily complex. Additionally, there is no test coverage for Node.js webpack bundles. The Next.js edge bundler tests also had limited OTel package coverage.

Depends on #6481

Short description of the changes

• Simplify existing browser webpack 4/5 bundler tests: replace HTML/browser-based testing with programmatic bundle validation
• Add new Node.js webpack 4/5 bundler test packages (bundler-tests/node/webpack-4, bundler-tests/node/webpack-5)
• Expand OTel package coverage in the Next.js 15/16 edge bundler tests to match the webpack tests (api, api-logs, sdk-logs, exporter-logs-otlp-http)
• Assert known protobuf dynamic-require failures in nextjs-15-edge and node/webpack-4: tests now pass while the bug is present and will break when it is fixed, prompting cleanup

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• npm run test:bundle

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.73%. Comparing base (dc93ed4) to head (8848ca9).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6482   +/-   ##
=======================================
  Coverage   95.73%   95.73%           
=======================================
  Files         364      364           
  Lines       12104    12104           
  Branches     2887     2887           
=======================================
  Hits        11588    11588           
  Misses        516      516           

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[overbalance]

Putting back into Draft because #6481 didn't address all the webpack errors found with the new tests in this PR.

[pichlermarc]

thx! great to have node bundler tests too now 🙌